Electron discharge device



March 28, 1939. H. G. I UBszYNsKl ET AL 2,151,785

ELECTRON DISCHARGE DEVICE Filed June 25, 1938 INVENTORS ZYNSKI .CAIRNSPatented Mar. 28, 1939 PATENT OFFICE ELECTRON DISCHARGE DEVICE HansGerhard Lubszynski, Hillingdon,

Harold Miller, South Ealing, London, and John Edwin Ingliston Cairns,West Ealing, London, England, assignors to Electric and MusicalIndustries, Ltd., Hayes, Middlesex, England Application June 25, 1938,Serial No; 215,72()l In Great Britain June 26, 1937 11 Claims.

This invention relates to electron discharge devices. and particularlyto such devices provided with a photosensitive electrode structurecapable of emitting electrons which are focused on a target electrode.

In television transmitting systems it has been proposed to project anoptical image of a subject for transmission upon a photosensitivecathode and to focus the photoelectrons emanating from` the cathode upona target such as a mosaic electrode having a plurality of mutuallyinsulated elements which are scanned by a beam of electrons to restorethe elements of the mosaic electrode to a datum potential and togenerate in an associated signal plate signals. representative of theoptical image Which are suitable for transmission. In other electrondischarge devices it has also been proposedto project an optical imageonto a photosensitive cathode and to focus the photoelectrons emanatingtherefrom upon a target of the'fluorescent screen type. Such devices maybe employed as electron telescopes or as light transformers. In thesedevices it has been customary to deposit the photosensitive layer of thecathode upon a support such as a mica disc which is mounted in theenvelope of the device but such arrangements havebeen unsatisfactory inthat longer focal length lenses are required for focusing theopticalimage on the cathode and difficulty has been experiencedr inarranging the electrostatic focusing electrodes in proper relationshipwith the cathode.

It is the principal' object of the present invention toprovide animproved electron discharge device employing a photosensitive cathode inwhich the above disadvantages lare avoided and with a view to improvingthe construction and simplifying the manufacture of the device.

In accordance with our invention an electron discharge device employinga photosensitive cathode is provided wherein the endv of the envelopewhich supports the photosensitive cathode is provided With a re-entrantsubstantially cylindrical portion and within the v cylindrical portionof i which there is provided a light transmitting plate or window on theinner surface on which or adjacent thereto the photosensitive layer isprovided. The Window may be of glass and when provided with thephotosensitive layer is preferably sealed in position in the cylindricalportion before the photosensitive layer is applied thereto. A ringshapedelectrode is mounted adjacent the photosensitive cathode and, inthepreferred form, the said electrode may be formed by silvering thesurface of the cylindrical re-entrant. portion in the interior of theenvelope, such portion preferably extending slightly beyond the plate orwindow on which the photosensitive layer is formed, the'silveringextending over the projecting edges of the cylindrical portion and incontact with the photosensitive layer.

A better understanding of our invention will be obtained and otherobjects, features, and advantages Will appear from the followingdescription taken in connection with the drawing in which: l0

Figure 1 is a longitudinal sectional View 'of an electron dischargedevice incorporating our invention; l

Figure 2 is a fragmentary View of a portion of structure shown in Figure1,

Figure 3 is a fragmentary sectional View of a modification of ourinvention, andV Figures 4 and 5 are fragmentary sectional views offurther modifications of our invention.

Referring to Figure 1, which shows an electron discharge device of thevlight transformer type, the envelope or bulb l preferably made of glass,has at one end a photosensitive cathode 2 and at the opposite end auorescent screen 3 on which electrons from the photocathode may befocused by the combined action of the electrostatic focusing fieldsgenerated by the anodes 4 and 5. The end of the bulb I enclosing thephoto-sensitive cathode 2 is, in accordance with our invention,provided. with a 12e-entrant open` ended cylindrical 30 portion 6 whichis tubular and extends inwardly of the bulb I. The re-entrant portion ismade of insulating material such as glass, and is closed adjacent itsinner or open end by a light transmitting window l which may be in theform of a glass plate, the said window, in the modification shown inFigure 1, having on its inner surface the photosensitive cathode 2referred to above. The photocathode 2Y is preferably of the translucenttype so that an optical image such as represented by the arrow 8 may befocused thereon through the Window 1 by the lens System 9. Surroundingthe window 1 and preferably extending around that section of thecylindrical re-entrant portion 6 which extends within the envelope fromthe 45 window, there is provided a ring-shaped electrode l0 which is inelectrical contact with the photosensitive cathode 2. This electrode maybe formed of thin sheet metal as shown in Figure 1 but may be made asshown in the fragmentary View of Figure 2 by metallizing the surface ofthe cylindrical 1re-entrant portion which extends beyond the Window l,the metallizing such as a lm of silver preferably extending over theprojecting edge of the re-entrant portion. The ring-shaped electrodeII), if formed by metallizing the desired section of the re-entrantportion 6, is preferably formed after the window I has been sealed tothe re-entrant portion but prior to the formation of the photosensitivecathode 2.

The photosensitive cathode 2 may be formed, as well known in the art, bydepositing on the interior surface of the Window 'I a very thin lm ofsilver which is oxidized and photo-sensitized by depositing caesum orother alkali metal thereon followed by proper heat treatment to increasethe photosensitivity of the cathode to a maximum value.

'Ihe anodes 4 and 5y are preferably of electrically conducting materialand may be of silver or of platinum deposited directly on thecylindrical wall of the envelope. The anode 4 preferably encloses abouthalf of the tubular re-entrant portion and is in telescopic relationtherewith for the purpose of providing a more uniform electrostatici'leld around the cathode. Leads I I and I2 connected such as by weldingto the anodes 4 and 5 respectively, extend through the cylindrical wallof the bulb I and are provided for the purpose of impressing suitableoperating potentials on the anodes 4 and 5 to focus electrons from thephotocathode 2 upon the fluorescent screen 3. The lead I3 is similarlyconnected to the ring-shaped electrode I and in the present constructionmay be brought to the exterior of the envelope without effecting theelectrostatic eld generated during the operation of the device by thecooperative action of the potentials applied between the cathode 2through the said lead I3 and the anode 4. This arrangement also permitsthe lens 9 to be made of a shorter focal length for focusing the opticalimage onto the cathode since the lens can be disposed closer to thecathode than in known constructions; in addition, the presentarrangement is generally of a more simplified construction compared withthe known devices.

In some cases instead of forming the photosensitive layer directly onthe glass wall or window 7, the photosensitive cathode 2 may be formedas shown in Figure 3 on an additional transparent support, such as asheet of mica I4, which is mounted in position adjacent the innersurface of the glass plate window 'I in the re-entrant portion.Furthermore, in some cases the ring electrode I0 may be preformed andapplied to the cylindrical portion of the re-entrant stem, and in suchcase the ring electrode so formed may serve to maintain the mica platecarrying the photosensitive layer in position.

In some applications and especially in those applications wheremono-chromatic sensitivity of the cathode is desired we provide a novellight filter fo-r filtering the light projected onto the photosensitivecathode. A further glass plate I5 or additional window may be providedin the reentrant portion, the plate I5 being suitably sealed in positionand spaced from the window 'I upon which the photosensitive cathode ispreferably formed, the space between the two walls being filled with asuitable solution I6 according to the filter required. If thephoto-sensitive cathode is more sensitive to the red portion of thespectrum the solution I6 may be a solution of copper sulphate whichaccentuates the sensitivity of Ithe cathode in the green portion of thespectrum.

Instead of forming the window 'I of glass it may be formed of variousother materials, particularly in cases Where the photo-sensitive cathodeis intended to be excited by the projection thereon of invisibleradiation. The term Window is therefore to be construed broadly and notto be limited to cases in which transparent substances are employed.

Figure 4 of the drawing illustrates a further form of the invention inwhich the photo-sensitive cathode is formed on a sheet of transparentmaterial I4, such as mica, which is supported adjacent to the Window 'Iand carried on the re-entrant portion 6 through the medium of a pair ofrings II and I8. The metal rings are held together with thephoto-sensitive cathode between them by a plurality of clamping membersI9 one of which is shown in Figure 4. 'I'he clamping members preferablyeach comprise a piece of `metal which is bent over, as shown in Figure4, to embrace the edge of the upper ring I'I and which is riveted tovthe lower ring I8 so as to clamp the two rings together with thephoto-sensitive cathode between them. Preferably, three of said clampingmembers are provided equi-distantly arranged. The lower ends of theclamping members are bent as indicated at 20 and these bent portions 20serve to locate the clamping rings and the photo-sensitive cathoderelatively to the window 'I and within the end of the re-entrant portion6 which projects beyond the window 1, as shown. In order to retain theunitary structure constituted by the rings II and I8 and the cathode I4in the position shown, a plurality of hooks 2| are provided, one ofwhich is shown in Figure 4. Preferably, three of the hooks are employeddisposed intermediate each clamping member I9 the hooks 2| co-operatingwith springs 22, one of which is shown in Figure 4, and which aresecured in glass seals 23. The hooks 2| and the springs 22 thus servesecurely to retain the photo-sensitive cathode in its position adjacentthe window 1, as shown in Figure 4. The ring I'I constitutes theequivalent of the electrode I0 of Figure 1 and in order to secure goodelectrical contact between the ring I1 and the photo-sensitive cathodethe mica plate I4 on which the cathode is formed may be provided with asilvered annulus I'Ia with which the ring I'I engages, thephoto-sensitive cathode being deposited after the plate I 4 is mountedbetween the rings I'I and I3 and a connection to the exterior of theenvelope may be established through the hooks 2| and the springs 22.

In the embodiment of the invention shown in Figure 5, the mica plate I4on which the photosensitive layer is formed is mounted directly againstthe end of the re-entrant portion 6, as shown, and is held in positionthere by a metal ring 24 provided with an inwardly projecting obliqueannular flange 25. In contact with the edge of the plate I4 is a helix2E which abuts against the inner surface of the ange 25, the ring 24forcing the helix 26 into contact with the plate I4 through the mediumof the flange 25 under the action of a plurality of springs 22 connectedto hooks 2| attached to the ring 24 similar to the arrangement of Figure4. The ring 24 also serves as the aforesaid electrode and the plate I4may be provided with a silver annulus I'Ia with which the helix 26 makeselectrical contact. It will be observed from Figure 5 that the end ofthe reentrant portion 6 fits into the ring 24 so that lateraldisplacement of the ring with respect to the re-entrant portion isprevented.

The kind of filter shown in Figure 1 may, if desired, be applied to theconstructions shown in Figures 4 or 5.

In manufacturing the device the re-entrant portion 6 is convenientlyformed separately from the envelope or bulb I and after the glass platesor windows are sealed in position in the re-entrant portion, the latteris sealed to the bulb.

While we have indicated the preferred embodiments of our invention ofwhich we are now aware and have indicated the specific application asdirected to an electron discharge device of the light transformer type,it will be apparent that our invention is by no means limited to theexact forms illustrated or to the use of our invention in electrondischarge devices of the type indicated, but that many variations may bemade in the particular structure and the applications for which it isemployed, such as in tubes utilizing a photosensitive cathode and amosaic electrode wherein the mosaic electrode is scanned by a beam ofincident energy, such as a light beam or beam of cathode rays, withoutdeparting from the scope of our invention as set forth in the appendedclaims.

We claim:

l. An electron discharge device having an envelope open at one end, aninwardly flared portion of smaller diameter than said envelope sealed tosaid envelope .at said open end, a window extending transversely acrossand sealed to said inwardly ared portion at a point slightly removedfrom the inner end of said portion, and a photosensitive cathode betweensaid window and said inner end of said portion.

2. An electron discharge device including an envelope, an inwardlyextending open ended tube integrally sealed tosaid envelope, a lighttransparent window sealed to said tube at a point slightly removed fromthe open end of said tube, a photosensitive coating on the inner surfaceof said window and an electrode between said window and the open end ofsaid tube and extending over the open edge of said tube electricallyconnected to said photosensitive coating.

3. An electron discharge device having an envelope, an inwardlyextending tube .at one end of` and sealed to the Wall of said envelope,a window in said tube extending transversely thereof and sealed to saidtube at a point slightly removed from the end of said tube opposite theend sealed to said wall, a photosensitive cathode between said windowand the open end of said tube, a second window between said rstmentioned window and the said wall of the envelope and a light filterbetween said windows.

4. An electron discharge device including an evacuated envelope, an openended tubular member sealed to one end of said envelope and extendinginwardly of said envelope, a plurality of windows sealed transversely tosaid tubular member between said open end and the opposite end of saidtubular member, a photosensitive cathode between the window adjacentsaid open end and the open end of said tubular member, a

ring-shaped electrode connected to said cathode and surrounding the openend of said tubular member and an anode on the wall of said envelope intelescopic relationship with said open ended tubular member.

5. An electron discharge device comprising an envelope, a re-entrantportion at one end of said envelope, a light transmitting window in saidre-entrant portion and a photo-sensitive cathode comprising a platemounted within said envelope and means supporting said plate on there-entrant portion adjacent to said Window.

6. An electron discharge device according to claim 5 wherein thephoto-sensitive cathode is supported directly on the window through themedium of a conducting electrode in electrical contact with thephoto-sensitive cathode.

7. An electron discharge device comprising an envelope, a re-entrantportion .at one end of said envelope, a light transmitting window insaid re-entrant portion, a pair of annular rings supported by saidtransparent portion, a photosensitive cathode supported between saidrings and means maintaining said rings in compression against saidtransparent portion.

8. An electron discharge device according to claim 'l wherein the saidmeans comp-rises leads of resilient material sealed in said envelope.

9. An electron discharge device comprising an envelope, a re-entrantportion at one end of said envelope, a light transmitting window in saidre-entrant portion between said one end of the envelope and the innerend of said re-entrant portion, a light transparent plate of largerdiameter than the internal diameter of said reentrant portion adjacentthe inner end of said re-entrant portion, a photosensitive cathode onthe side of said plate opposite the inner end of said `re-entrantportion, and resilient means maintaining said photocathode against saidreentrant portion.

10. An electron discharge device including an envelope, an inwardlyextending open-ended tube integrally sealed to said envelope, a lighttransparent window sealed to said tube at a point slightly removed fromthe open end of said tube, .a photosensitive cathode supported on theinner end of said tube, a metallic ring surrounding the. end of saidtube, a second ring supported by said rst ring, and a helix between saidrings and said cathode maintaining said cathode against the open end ofsaid tube.

11. An electron discharge device according to claim wherein the said rstmentioned ring is held in position by resilient leads connected to saidring and to the envelope of the device.

HANS GERHARD LU'BSZYNSKI. HAROLD MILLER. JOHN EDWIN INGLISTON CAIRNS.

